Neon signs require about 12,000 v for their operation. consider a neon-sign transformer that operates off 120- v lines. how many more turns should be on the secondary compared with the primary?

I can't give you the actual number of turns, because it's the RATIO
that counts. 

However many turns the primary has, the secondary should have
about TEN TIMES that number.  Then the transformer will multiply
the primary voltage by 10 ... 120 volts of AC at the primary will
become 1,200 volts of AC at the secondary.

Note that it HAS TO be AC.  If the transformer is supplied with DC,
then 120 volts at the primary becomes zero volts at the secondary
and a big cloud of stinky smoke in the room.